Metal composition



Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE METAL COMPOSITION NoDrawing.

1 Claim.

This invention relates to tungsten metal compositions particularly thosesuitable for electrical contact purposes.

It is an object of this invention to improve the characteristics oftungsten metal compositions having a high melting point.

It is a further object of this invention to produce a material whichwill retain a low contact resistance during long periods of operation.

Other objects of the invention will be apparent from the followingdescription taken in connection with the appended claim.

The present invention comprises the combination of elements, methods ofmanufacture, and

the product thereof brought out and exemplified in the disclosure,hereinafter set forth, the scope of the invention being indicated in theappended claim. I

In the prior art, ma'ny contact materials and electrodes have beenproposed which supposedly give good electrical conductivity andsuflicient resistance against wear and oxidation. Metals which have beenused for contact purposes, for instance,- were silver, copper, platinum,tungsten,

'33 or alloys and metal compositions which consist principally oftungsten and copper, plus tungsten and silver. Recently also alloys orcompositions consisting of molybdenum carbide and silver or copper, havebeen proposed.

.10 In the course of my investigation I have discovered that by addingmetals having a very high vapor pressure at comparatively lowtemperatures to a refractory base excellent contacting materials couldbe produced. I have found that :13 the boiling point of the metals whichare most desirable for alloying with a refractory base should be below1000 degrees C. The materials which suit this condition best are cadmiumand zinc. and of the two, cadmium has the lowest boiling point and showsthe best characteristics when used in connection with a refractory basefor contact purposes;

According to the present invention, I therefore provide a metalcomposition of tungsten, a'metal oi the group consisting of cadmium andzinc, and silver. The above mentioned ingredients can be used in thefollowing permissible range of proportions:

Per cent Tungsten 40 to '70 Metal of the group consisting of zinc andcadmium 0.5 to 5 Silver Balance.

I have found that small percentages of such Application September 22,1937, Serial No. 165,170

metals as iron, cobalt, nickel and manganese may be present withoutmaterially changing the characteristics of this new contacting material.It is also possible that small quantities of a noble metal taken fromthe palladium or platinum 5 group may be included in the composition.

Compositions of the type contemplated can be made by mixing tungsten andsilver very intimately, and then pressing them to a high density. Thepressed bars are sintered in a hydrogen 10 furnace, and after sintering,they are impregnated with either zinc or cadmium. This may be done byplacing zinc or cadmium on top of the pressed bar and stoking it throughthe furnace at a temperature of 650 to 750 degrees C. If cadmium isbeing used, then the preferred temperature is 650 degree C., on accountof the low boiling point of cadmium. In the case of zinc. thistemperature may be increased to 750 degrees C. or slightly higher.

The advantage of such a metal composition to which substantialquantities of cadmium have been added, consists in the property ofcadmium to prevent the excess formation of metallic oxides which areusually encountered in contact applications. Due to the contact arcs orcontact sparks, very high local temperatures are reached in certainplaces on the contact. The contact arc or contact spark ionized theairand the oxygen and nitrogen of the air are very active in forming oxidesor other compounds with the contact metals. These oxides have usually avery high contact resistance. A scientific explanation of the action ofcadmium has not been thoroughly studied, but actual tests have shownthat under the same test conditions, a material prepared according tothis disclosure will show a contact resistance which is only a fractionof that of the materials used without the addition of cadmium. It ispossible that the action of cadmium can be explained on account of thedissociation of cadmium oxide at red heat or it is possible that thecontact spark and arc are deionized, which increases the life of thecontacting members.

Several methods of manufacture are possible to produce metallic bodiesof the nature described. In addition to the method already cited it ispossible to produce silver-cadmium alloys which have a very low meltingpoint and which might be used for impregnating the tungsten base. Itmight be found necessary-to add special ingredients which will lower themelting point of such materials to below 500 degrees C. Elements whichare helpful in that respect are magnesium, phosphorus, arsenic,antimony, germanium, indium.

It is also possible to take the various powders, such as tungstenpowder, silver powder and cadmium powder and press same together undervery high pressure. It has been found possible, under certainconditions, to compress the materials at an elevated temperature, andthe temperature range in which the best results were obtained is from100 to approximately 500 degrees C. If such elevated temperatures areused and pressure is applied, then -a much denser product will beobtained because the yield point, or the flow" point of the metalpowders is lowered sufiiciently to produce an actual amount of colddeformation and instantaneous recrystallization. Such recrystallizationwill cement the various powders very tightly together and the materialis subsequently heated, diffusion will proceed very rapidly and aperfect material can be obtained.

Under certain conditions, it has also been found advisable to eitherimpregnate or sinter the metal body containing cadmium under pressure.This will materially decrease the loss of cadmium due to avolatilization. A container can be made out of a special steel or anickelchromium alloy, which is heat resistant. During sintering at atemperature higher than the boiling point-of either cadmium or zinc,part of the latter two elements are volatilized and exert sumcientpressure to prevent further volatilize.- tion at this particulartemperature.

It is contemplated that other ingredients may be present in thecompositions, either as impurities or as diluents which do notmaterially aifect the important properties of the material, while stillfollowing the present invention.

While the present invention as to its objects has been described hereinas carried out in specific embodiments thereof, it is not desired to belimited thereby, but it is intended to cover the invention broadlywithin the spirit and scope of the appended claim.

What is claimed is:

A metal composition wherein a mass of substantially non-alloyingparticles of tungsten are bonded by an alloy of lower melting point thansaid tungsten, said composition containing 40% to 70% tungsten, from0.5% to 5% of metal selected from the group consisting of cadmium andzinc, balance substantially all silver.

FRANZ R. HENSEL.

